How is shelf cloud, which was seen in viral video from Uttarakhand, formed?

A shelf cloud or Arcus cloud, which was recently seen in Uttarakhand, forms when cold air hits the ground ahead of a storm. That cold, dry air then encounters warm, moist air and forces the warm air up, creating both downward and upward draft. The combination of those two drafts spins the clouds into the patterns associated with shelf clouds.